The clear trend in the computer industry today is toward the further development of portable computer systems. For example, notebook computers, laptop computers, and pen-based portable computers are becoming increasingly popular and have already enjoyed widespread success in the marketplace. In many cases, these computer systems are designed to operate utilizing a power supply potential generated by a battery. Because of the continuous power drain associated with battery-powered systems there has been an emphasis on developing circuits and systems which are either capable of operating at reduced power levels, or which feature a low-power mode of operation. Disk drive systems are presently manufactured to operate at voltages of either 3.0 or 5.0 volts.
One of the problems that arises in disk drive systems is that the performance of the drive changes radically as the power supply voltage fluctuates. Typically, when the power supply voltage level drops, the amount of current that can be supplied to the actuator decreases correspondingly. This results in longer access times due to the shortage of available power when performing a seek operation. Even though many servo circuits in a disk drive are capable of operating within a power supply voltage range of 3.0 to 5.0 volts, most disk drive systems are generally limited to operating under a specific power supply voltage matched to a predetermined set of seek and reset parameters.
For example, if a rigid-disk drive is intended to be operated with a 5.0 volt power supply voltage, the seek and reset parameters of the drive will normally be specified based upon the amount of current available with a 5.0 volt supply level. If the supply voltage drops below a certain minimum level (e.g., 4.2 volts) a reset condition is generated to disable the drive. This places a serious limitation on portable computer systems since it is often desired to continue computing--albeit with reduced performance parameters--even though the voltage of the drive has dropped below the normal reset voltage associated with the 5.0 volt supply potential. In other words, it is desirable to have a disk drive system adaptable to multiple supply voltages, or that could adjust its performance dynamically in accordance with variations to the operating power supply potential. Such a drive would be able to sense supply potential changes within an expected operating range and adjust its seek and reset parameters accordingly. This would enable the disk drive to continue operating under power supply conditions that would normally cause prior art drives to either malfunction or experience destructive breakdown.